For West Prussia (and Ost/East Prussia) and Schlesien (Silesia): http://www.kartenmeister.com/preview/databaseuwe.asp
The maps are from the Ludwig Ravenstein series -- he (his company) made very detailed maps of the entire Prussian Empire for decades. The maps at the Kartenmeister site are from about 1905.

For locations anywhere in the German/Prussian Empire, try these sites:

1883 Ravenstein map and gazetteer (place name index): http://www.library.wisc.edu/etext/ravenstein/
or http://gov.genealogy.net/index.jsp
The search works with either present-day (e.g. Polish) names or old German names. The map display is in present-day (Polish) terms.

[Note: if you are using "dial-up" for email and internet connections, then the maps and name indexes will take a long time to download, because each page is quite large.]